Memory array

ABSTRACT

A memory array used in the field of semiconductor technology includes a plurality of memory cells, bit lines, word lines perpendicular to the bit lines, and first/second control lines. The memory array uses split-gate memory cells, wherein two memory bit cells of a memory cell share one word line, thereby the read, program and erase of the memory cell can be realized by applying different voltages to the word line, two control gates and source/drain regions; the word line sharing structure enables a split-gate flash memory to effectively reduce the chip area and avoid over-erase problems while maintaining electrical isolation performance of the chip unchanged and not increasing the complexity of the process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/253,855, filed Oct. 5, 2011, which in turn claims the priority toChinese patent application number 201110035558.X, filed on Feb. 10,2011, the entire contents of both of which are incorporated herein byreference for all purposes.

TECHNICAL FIELD

The present invention relates to a memory array, in particular, relatesto a memory array of split-gate flash memory structures and itsprogramming method.

BACKGROUND

Flash memory has become a research hot spot in non-volatile memories forits advantages of convenience, high storage density and goodreliability. With developments of technology and storage requirements ofelectronic products, flash memory has been widely used in mobile andcommunication devices, such as mobile phones, laptop computers, PDAs andUSB flash drives. Flash memory, as a kind of non-volatile memory, isoperated by modifying the threshold voltage of the transistor or memorycell to control the on/off state of the channel, so as to realize thestorage of data and ensures that the data stored in the memory will notbe lost in case of power outage. Flash memory is also a specialstructure of electrically erasable programmable read-only memory.Currently, flash memory has occupied most of the market share ofnon-volatile semiconductor memories and has become a non-volatilesemiconductor memory with the fastest developing speed.

However, when the existing flash memories are developing towards ahigher storage density, it is difficult to increase the storage densityby reducing the size of the device due to the restriction of theprogramming voltage. Moreover, further reducing the programming voltageof the device is facing great challenges due to the limitation of thestructure. Generally, a flash memory is of a split gate type or astacked gate type, or a combination thereof. Compared to a stacked-gateflash memory, a split-gate flash memory has unique advantages inprogramming and erasing operations for its special structure, therefore,it is widely used due to its high programming efficiency and itsadvantage of avoiding over-erase owing to its word line structure.However, the split-gate flash memory has one more word line than thestacked-gate flash memory, which makes chip area increase. To introducememory cells with higher packaging density into a semiconductor memorydevice, the layout of memory device circuits with a smaller size must beused. Therefore, in order to solve the problems caused by high-densitypackaging of the memory cells, the structure of the semiconductor memorydevice must be improved.

So far, many attempts have been made to increase the density of memorycells. For example, EP0109853A2 disclosed an array of MOS transistorsformed on a semiconductor substrate with a plurality of bit linesserving as the source and drain regions of the MOS transistors, whereina plurality of conductive word lines are formed above the plurality ofbit lines, being insulated from and perpendicular to the bit lines, eachconductive word line serving as the gates of a plurality of MOStransistors. Each transistor of the memory array is formed in a regioncontaining two bit lines and a single word line and forms a contact witheach bit line. To avoid danger and reduce the capacitance betweenconductive lines, a thin film of field oxide is formed on bit lines toisolate the bit lines from the polysilicon lines. In addition,generally, between adjacent bit lines and adjacent polysilicon lines, athick layer of field oxide is needed to isolate a memory cell from itsadjacent cell, so as to minimize point coupling between them. As eachbit line is connected to a conductive metal contact line, metal linesmust be formed intensively on a single semiconductor wafer, and theincrease of cell density will correspondingly increase the intensity ofmetal lines, as a result, the complexity and cost of the manufacturingprocess is largely increased because lines with very small criticaldimensions need to be formed during the photolithography and etchprocesses. Therefore, such method for increasing density of memory cellshas high requirements on process conditions and is not suitable forpopularization and promotion.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a memory array whichcan effectively reduce the area of a chip and simultaneously can avoidover-erase problems while maintaining the electrical isolationperformance of the chip unchanged, so as to solve the problem ofrequiring a very advanced technology to increase the density of a memoryarray in the prior art.

To achieve the above objective, the memory array of the presentinvention comprises: a plurality of memory cells, a plurality ofparalleled bit lines formed on a semiconductor substrate, and aplurality of word lines perpendicular to the bit lines, wherein each bitline is connected to a source and a drain of adjacent memory cells,while a part of a word line between adjacent bit lines is connected to agate of a memory cell. In the memory array, the memory cells aresplit-gate memory cells, each including a first memory bit cell arrangedbetween the word line and a source of the memory cell, and a secondmemory bit cell arranged between the word line and a drain of the memorycell, the first and second memory bit cells comprising a first controlgate and a second control gate, respectively; the memory array furthercomprises a plurality of first control lines and second control linesconnected to the first and the second control gates, respectively, eachpair of the first and the second control lines being arranged on bothsides of a word line and being parallel to the word line.

Furthermore, a part of a bit line forms the source and the drain ofadjacent memory cells connected to the bit line; a part of a word lineforms the gate of the memory cell connected to the word line.

Furthermore, the first memory bit cell further comprises a firstfloating gate, the first control gate is spaced from and arranged abovethe first floating gate; the second memory bit cell further comprises asecond floating gate, the second control gate is spaced from andarranged above the second floating gate.

Furthermore, the part of the word line forming the gate of a memory cellis isolated from the semiconductor substrate, the first floating gateand second floating gate by a tunneling oxide layer; gate oxide layersare formed between the first floating gate and the semiconductorsubstrate, as well as between the second floating gate and thesemiconductor substrate.

Furthermore, the tunneling oxide layer has a thickness from 80 Å to 200Å, and the gate oxide layers formed between the part of the word lineforming the gate of a memory cell and the semiconductor substrate have athickness from 80 Å to 200 Å.

Furthermore, interlayer dielectric films are formed between the firstfloating gate and the first control gate, between the second floatinggate and the second control gate, as well as between the word line andthe first and second control gates.

Furthermore, the interlayer dielectric films are insulating dielectricfilms formed by one of silicon dioxide, silicon nitride, siliconoxynitride, carbon-containing silicon oxide or any combination structurethereof.

Furthermore, both the first and the second floating gates arepolysilicon floating gates, silicon nitride floating gates ornano-crystal materials having electrical conductivity; both the firstand second control gates are polysilicon control gates or metal controlgates; the word lines are polysilicon selection gates or metal selectiongates.

Furthermore, the word line, the first and second control lines are allarranged below or above the bit lines.

Furthermore, the first and the second memory bit cells share one wordline, operating voltages are applied to the word line, the first controlgates, the second control gate, and the bit lines connected to thesource and the drain to read, program and erase the memory bit cells.

Alternatively, the first and the second memory bit cells erase electriccharges by applying a high voltage to the word line. And furthermore,both the first and the second control gates of the memory cells arepolysilicon control gates, when the word line is polysilicon selectiongate, both the first and second memory bit cells use a poly to polyerase.

When performing an erasing operation to the first and the second memorybit cells, the erasing voltage applied to the word line is from 9 V to12 V, and preferably 11V.

Alternatively, both the first and the second memory bit cells eraseelectric charges by applying a high voltage to the word line andapplying a negative voltage to the first/second control gate, the highvoltage applied to the word lines is from 5 V to 10 V, preferably 8 V;the negative voltage applied to the first/second control gate is from −5V to −10 V, preferably −7 V.

Furthermore, the first and the second memory bit cells are programmed byhot electron injection. During a programming operation to the firstmemory bit cell, programming voltages applied to the word line, thefirst control gate, the second control gate, the bit line connected tothe source and the bit line connected to the drain are from 1 V to 2 V,from 5 V to 11 V, from 2 V to 6 V, from 2.5 V to 5.5 V and from 0 V to0.6 V, and preferably 1.5 V, 10 V, 4 V, 5 V and 0 V respectively; duringthe programming operation to the second memory bit cell, the programmingvoltages applied to the word line, the first control gate, the secondcontrol gate, the bit line connected to the source and the bit lineconnected to the drain are from 1 V to 2 V, from 2 V to 6 V, from 5 V to11 V, from 0 V to 0.6 V and from 2.5 V to 5.5 V, and preferably 1.5 V, 4V, 10 V, 0 V and 5 V, respectively.

Furthermore, during a reading operation to the first memory bit cell,reading voltages applied to the word line, the first control gate, thesecond control gate, the bit line connected to the source and the bitline connected to the drain are from 0.5 V to 5 V, from 0 V to 3 V, from0 V to 6 V, from 0 V to 0.5 V and from 0.8 V to 3 V, and preferably 2.5V, 2.5 V, 4 V, 0 V and 2 V, respectively; during the reading operationto the second memory bit cell, the reading voltages applied to the wordline, the first control gate, the second control gate, the bit lineconnected to the source and the bit line connected to the drain are from0.5 V to 5 V, from 0 V to 6 V, from 0 V to 3 V, from 0.8 V to 3 V andfrom 0 V to 0.5 V, and preferably 3 V, 3 V, 2.5 V, 2 V and 0.5 V,respectively.

The advantages of the present invention are as follows: a bit line of amemory array is shared by a source and a drain of adjacent transistors,and a part of a word line forms a gate of a memory cell connected to theword line, moreover, the memory array of the present invention usessplit-gate memory cells, wherein two memory bit cells of a memory cellshare a word line, thereby the read, program and erase of the memorycell can be realized by applying different voltages to the word line,two control gates, and source/drain regions; the word line sharingstructure enables a split-gate flash memory to effectively reduce thechip area while maintaining the electrical isolation performance of thechip unchanged and simultaneously avoiding the over-erase problems, andnot increasing the complexity of the process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the memory array according to thepresent invention;

FIG. 2 is a schematic diagram of the semiconductor structure of memorycells in a memory array according to the present invention;

FIG. 3 is a specific schematic diagram showing the connections of amemory cell in a memory array according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In order to make the purpose, technical solution and advantages of thepresent invention clearer, the present invention is further detailed incombination with the accompanying drawings.

FIG. 1 is a schematic diagram of the memory array according to thepresent invention.

As shown in FIG. 1, the memory array according to the present inventioncomprises:

one or more memory cells;

a plurality of paralleled bit lines BL formed on the semiconductorsubstrate;

a plurality of word lines WL perpendicular to the bit lines.

wherein, each bit line BL is connected to a source of one memory celland a drain of another memory cell adjacent to the one memory cell, apart of a word line WL between adjacent bit lines BL is connected to agate of a memory cell.

FIG. 2 is a schematic diagram of the semiconductor structure of memorycells in a memory array according to the present invention.

As shown in FIG. 2, in a memory array according to the presentinvention, a memory cell 100 is a split-gate memory cell, comprising:

a semiconductor substrate 10;

a first active region 11 and a second active region 12 arranged in thesemiconductor substrate 10 and spaced apart from each other, in thepresent embodiment, the first active region 11 is a source doping regionS and the second active region 12 is a drain doping region D, the firstand second active regions 11 and 12 are respectively picked up byadjacent bit lines of the memory array to connect with externalelectrodes;

a first memory bit cell 110 formed between a word line 303 and the firstactive region 11 (i.e. the source doping region S), comprising a firstfloating gate 101 and a first control gate 102, the first control gate102 being spaced from and arranged above the first floating gate 101,the first floating gate 101 being connected to an external electrode bya first control line CG1 of the memory array;

a second memory bit cell 210 formed between the word line 303 and thesecond active region 12 (i.e. the drain doping region D), comprising asecond floating gate 201 and a second control gate 202, the secondcontrol gate 202 being spaced from and arranged above the secondfloating gate 201, the second floating gate 201 being connected to anexternal electrode by a second control line CG2 of the memory array.

In the present embodiment, the word line 303 is isolated from thefirst/second floating gate 101/102 of the memory cell 100 and thesemiconductor substrate 10 by a tunneling oxide layer 311.

In the present embodiment, the first floating gate 101 of the memorycell 100 is isolate from the semiconductor substrate 10 by a gate oxidelayer 111 with a thickness from 60 Å to 150 Å; the first floating gate101 is isolated from the first control gate 102 by an interlayerdielectric film 112, the interlayer dielectric film 112 is an insulatingdielectric film with a thickness from 60 Å to 350 Å formed by one ofsilicon oxide, silicon nitride, silicon oxynitride, carbon-containingsilicon oxide or any combination structure thereof.

In the present embodiment, the second floating gate 201 of the memorycell 100 is isolated from the semiconductor substrate 10 by a gate oxidelayer 211 with a thickness from 60 Å to 150 Å; the second floating gate201 is isolated from the second control gate 202 by an interlayerdielectric film 212, the interlayer dielectric film 212 is an insulatingdielectric film with a thickness from 60 Å to 350 Å formed by one ofsilicon oxide, silicon nitride, silicon oxynitride, carbon-containingsilicon oxide or any combination structure thereof.

The first control line CG1 and the second control line CG2 are arrangedin a same dielectric layer with the word line WL; the control lines CG1and CG2 are arranged on both sides of the word line WL and beingparallel to the word line.

In the present embodiment, the word line 303 of the memory cell 100comprises a first part 303 a and a second part 303 b, wherein the firstpart 303 a is arranged between the first memory bit cell 110 and thesecond memory bit cell 120 and forms the gate of the memory cell 100;the second part 303 b is above the first part 303 a and extends in bothsides, to cover the entire first memory bit cell 110 and the entiresecond memory bit cell 210.

In the present embodiment, the tunneling oxide layer 311 formed betweenthe word line 303 and the semiconductor substrate 10 as well as betweenthe word line 303 and the first/second floating gate 101/201 is asilicon oxide layer or a silicon nitride layer, or a combinationstructure thereof and has a thickness from 80 Å to 200 Å. The word line303 is isolated from the first/second control gates 102/202 byinterlayer dielectric films 313, the interlayer dielectric films 313 areinsulating dielectric films formed by one of silicon dioxide, siliconnitride, silicon oxynitride, carbon-containing silicon oxide or anycombination structure thereof, wherein the thickness of the interlayerdielectric films 313 is from 100 Å to 500 Å and should be larger thanthat of the tunneling oxide layer 311.

In the present embodiment, both the first floating gate 101 and thesecond floating gate 201 of the memory cell 100 are polysilicon floatinggates or silicon nitride floating gates or nano-crystal materials havingelectrical conductivity; both the first control gate 102 and the secondcontrol gate 202 are polysilicon control gates or metal control gates;the word line 303 is a polysilicon selection gate or a metal selectiongate; an insulating dielectric film 314 formed by one of silicondioxide, silicon nitride, silicon oxynitride, carbon-containing siliconoxide or any combination thereof is deposited on the surfaces and sidefaces of the first memory bit cell 110, the second memory bit cell 210,and the word line 303 to isolate them from the metal layer (not shown)connecting to the source/drain electrode; when the memory cell 100 is inoperation, the first/second memory bit cell 110/210 erases electriccharges by applying a high voltage to the word line 303 while theprogramming operation is performed in a way of hot electron injection.

As an alternative embodiment, the word line WL, the first control lineCG1, and the second control line CG2 of a memory array are all arrangedbelow the bit lines BL.

As another alternative embodiment, the word line WL, the first controlline CG1, and the second control line CG2 of a memory array are allarranged above the bit lines BL.

As a preferred embodiment, in a memory array, both the first floatinggate 101 and the second floating gate 201 of the memory cell 100 arepolysilicon floating gates; both the first control gate 102 and thesecond control gate 202 are polysilicon control gates; the word line 303is a polysilicon selection gate; the tunneling oxide layer 311 formedbetween the word line 303 and the semiconductor substrate 10 as well asbetween the word line 303 and the first/second floating gate 101/201 isa silicon oxide layer and has a thickness of 100 Å; the gate oxide layer111/211 formed between the first/second floating gate 101/201 and thesemiconductor substrate 10 has a thickness of 80 Å; the interlayerdielectric film 112/212 between the first/second floating gate 101/201and the first/second control gate 102/202 is formed by silicon nitrideand has a thickness of 120 Å; the interlayer dielectric film 313 betweenthe word line 303 and the first/second control gate 102/202 is formed bysilicon nitride and has a thickness of 200 Å; meanwhile, thefirst/second memory bit cell 110/120 uses the method of poly to polyerase to reduce the erasing voltage.

As an alternative embodiment, in a memory array, both the first floatinggate 101 and the second floating gate 201 of the memory cell 100 aresilicon nitride floating gates; both the first control gate 102 and thesecond control gate 202 are polysilicon control gates; the word line 303is a polysilicon selection gate; the tunneling oxide layer 311 betweenthe word line 303 and the semiconductor substrate 10 as well as betweenthe word line 303 and the first/second floating gate 101/201 is formedby a stacked structure of silicon dioxide layer and silicon nitridelayer and has a thickness of 120 Å; the gate oxide layer 111/211 formedbetween the first/second floating gate 101/201 and the semiconductorsubstrate 10 has a thickness of 90 Å; the interlayer dielectric film112/212 between the first/second floating gate 101/201 and thefirst/second control gate 102/202 is formed by silicon dioxide and has athickness of 180 Å; the interlayer dielectric film 313 between the wordline 303 and the first/second control gate 102/202 is also formed bysilicon dioxide and has a thickness of 300 Å.

As another alternative embodiment, in a memory array, both the firstfloating gate 101 and the second floating gate 201 of the memory cell100 are nano-crystal floating gates; both the first control gate 102 andthe second control gate 202 are polysilicon control gates; the word line303 is a metal selection gate; the tunneling oxide layer 311 between theword line 303 and the semiconductor substrate 10 as well as between theword line 303 and the first/second floating gate 101/201 is formed by asilicon oxide layer and has a thickness of 150 Å; the gate oxide layer111/211 formed between the first/second floating gate 101/201 and thesemiconductor substrate 10 has a thickness of 130 Å; the interlayerdielectric film 112/212 between the first/second floating gate 101/201and the first/second control gate 102/202 is formed by a siliconoxynitride layer and has a thickness of 200 Å; the interlayer dielectricfilm 313 between the word line 303 and the first/second control gate102/202 is also formed by a silicon oxynitride layer and has a thicknessof 350 Å.

As yet another alternative embodiment, in a memory array, both the firstfloating gate 101 and the second floating gate 201 of the memory cell100 are silicon nitride floating gates; both the first control gate 102and the second control gate 202 are metal control gates; the word line303 is a metal selection gate; the tunneling oxide layer 311 between theword line 303 and the semiconductor substrate 10 as well as between theword line 303 and the first/second floating gate 101/201 is formed by astacked structure of silicon dioxide layer and silicon nitride layer andhas a thickness of 200 Å; the gate oxide layer 111/211 formed betweenthe first/second floating gate 101/201 and the semiconductor substrate10 has a thickness of 150 Å; the interlayer dielectric film 112/212between the first/second floating gate 101/201 and the first/secondcontrol gate 102/202 is formed by a stacked structure of silicon dioxidelayer, silicon nitride layer, and silicon oxynitride layer and has athickness of 200 Å; the interlayer dielectric film 313 between the wordline 303 and the first/second control gate 102/202 is also formed by astacked structure of silicon dioxide layer, silicon nitride layer, andsilicon oxynitride layer and has a thickness of 400 Å.

FIG. 3 is a specific schematic diagram showing the connections of amemory cell in a memory array according to the present invention.

As shown in FIG. 3, a memory cell comprises a first memory bit cell Bit1having a first control gate CG1 and a second memory bit cell Bit2 havinga second control gate CG2; a gate G of the memory cell is connected tothe word line WL, while a source S and a drain D of the memory cell arerespectively connected to the bit lines BL and BL+1.

As shown in FIG. 3, the first memory bit cell Bit1 and the second memorybit cell Bit2 of the memory cell share a word line WL; operatingvoltages are applied to the word line WL, the first control gate CG1,the second control gate CG2, the bit line BL connected to the source Sand the bit line BL+1 connected to the drain D to read, program anderase the memory bit cells.

In the present embodiment, both the first memory bit cell Bit1 and thesecond memory bit cell Bit2 erase electric charges by applying a highvoltage to the word line WL, wherein the high voltage applied to theword line WL is from 9 V to 12 V, as a preferred embodiment, the highvoltage is 11 V. Meanwhile, the voltage applied to the bit lines BL andBL+1 of the memory array is 0 V.

As an alternative embodiment, both the first memory bit cell Bit1 andthe second memory bit cell Bit2 erase electric charges by applyingvoltages to the word line WL and the control gate CG1/CG2, wherein ahigh voltage from 5 V to 10 V is applied to the word line WL, a negativevoltage from −5 V to −10 V is applied to the control gate CG1/CG2. As apreferred embodiment, during an erasing operation, voltages applied tothe word line WL, the first control gate CG1 and the second control gateCG2 are 8V, −7V and −7V respectively, the absolute value of the voltageapplied to the word line WL is reduced by applying a negative voltage tothe first/second control gate CG1/CG2. Meanwhile, a voltage of 0 V isapplied to all the bit lines in the memory array as shown in FIG. 1.

As a preferred embodiment, both the first control gate CG1 and thesecond control gate CG2 are polysilicon control gates, and the word lineWL is a polysilicon selection gate. Meanwhile, the first memory bit cellBit1 and the second memory bit cell Bit2 use the method of poly to polyerase.

In the present embodiment, a programming operation to both the firstmemory bit cell Bit1 and the second memory bit cell Bit2 is performed bythe method of hot electron injection.

In the present embodiment, during the programming operation to the firstmemory bit cell Bit1, programming voltages applied to the world line WL,the first control gate CG1, the second control gate CG2, the bit line BLconnected to the source S and the bit line BL+1 connected to the drain Dare from 1 V to 2 V, from 5 V to 11 V, from 2 V to 6 V, from 2.5 V to5.5 V and from 0 V to 0.6 V, respectively. In the memory array as shownin FIG. 1, a voltage of about 1.5V to 2.5V is applied to the bit linesBL−1, BL−2, . . . adjacent to the bit line BL connected to the source Sand all the bit lines>BL+3; a low voltage from 0.1 V to 0.6 V is appliedto the bit lines BL+2 and BL+3 adjacent to the bit line BL+1 connectedto the drain D.

As a preferred embodiment, the programming voltages for the programmingoperation to the first memory bit cell Bit1 are 1.5 V, 10 V, 4 V, 5 Vand 0 V, respectively.

As an alternative embodiment, the programming voltages for theprogramming operation to the first memory bit cell Bit1 are 1.4 V, 8 V,5 V, 4.5 V and 0.1 V, respectively.

In the present embodiment, during the programming operation to thesecond memory bit cell Bit2, programming voltages applied to the worldline WL, the first control gate CG1, the second control gate CG2, thebit line BL connected to the source S and the bit line BL+1 connected tothe drain D are from 1 V to 2 V, from 2 V to 6 V, from 5 V to 11 V, from0 V to 0.6 V and from 2.5 V to 5.5 V, respectively. Meanwhile, in thememory array as shown in FIG. 1, a low voltage from 0.1 V to 0.6 V isapplied to the bit lines BL−1 and BL−2 adjacent to the bit line BLconnected to the source S; a voltage of about 1.5V to 2.5V is applied tothe bit lines<BL−2 and the bit lines BL+2, BL+3, . . . adjacent to thebit line BL+1 connected to the drain D.

As a preferred embodiment, the programming voltages for programmingoperation to the second memory bit cell Bit2 are 1.5 V, 4 V, 10 V, 0 Vand 5 V, respectively.

As an alternative embodiment, the programming voltages for programmingoperation to the second memory bit cell Bit2 are 1.4 V, 5 V, 8 V, 0.1 Vand 5 V, respectively.

During a reading operation to the first memory bit cell Bit1, readingvoltages applied to the world line WL, the first control gate CG1, thesecond control gate CG2, the bit line BL connected to the source S andthe bit line BL+1 connected to the drain D are from 0.5 V to 5 V, from 0V to 3 V, from 0 V to 6 V, from 0 V to 0.5 V and from 0.8 V to 3 V,respectively. At this time, in the memory array as shown in FIG. 1,voltages of 0 V is only applied to the bit lines BL+2 and BL+3 adjacentto the bit line BL+1 connected to the drain D, and all the other bitlines are floating.

As a preferred embodiment, the reading voltages for reading operation tothe first memory bit cell Bit1 are 2 V, 2.5 V, 4 V, 0 V and 2 V,respectively.

As an alternative embodiment, the reading voltages for reading operationto the first memory bit cell Bit1 are 2.5 V, 0 V, 5 V, 0.5 V and 1 V,respectively.

During the reading operation to the second memory bit cell Bit2, readingvoltages applied to the world line WL, the first control gate CG1, thesecond control gate CG2, the bit line BL connected to the source S andthe bit line BL+1 connected to the drain D are from 0.5 V to 5 V, from 0V to 6 V, from 0 V to 3 V, from 0.8 V to 3 V and from 0 V to 0.5 V,respectively. At this time, in the memory array as shown in FIG. 1, avoltage of 0 V is applied to the bit lines BL−1 and BL−2 adjacent to thebit line BL connected to the source S, all the other bit lines arefloating.

As a preferred embodiment, the reading voltages for reading operation tothe second memory bit cell Bit2 are 3 V, 4 V, 2.5 V, 2 V and 0 V,respectively.

As an alternative embodiment, the reading voltages for reading operationto the second memory bit cell Bit2 are 4 V, 5 V, 0 V, 1 V and 0.5 V,respectively.

In the present embodiment, the bit lines BL of the memory array areshared by the source S and the drain D of adjacent transistors, and apart of a word line WL (303) forms the gate G of the memory cellconnected to the word line, moreover, the memory array according to thepresent embodiment uses split-gate memory cells, wherein two memory bitcells Bit1 and Bit2 of a memory cell share a word line WL, thereby theread and erase of the memory bit cells can be realized by applyingdifferent voltages to the word line WL, two control gates CG1 and CG2 aswell as the source and drain regions BL and BL+1; the program of thememory bit cells can be realized by hot electron injection. The wordline sharing structure enables a split-gate flash memory to effectivelyreduce the chip area while maintaining the electrical isolationperformance of the chip unchanged and simultaneously avoiding theover-erase problems. The memory array adopting the present memory cellstructure is much compacter in structure and can increase the density ofmemory bit cells without increasing the density of the metal lines orincreasing the complexity of the process, thus effectively increasingthe density of the memory array and reducing the chip area.

Numerous embodiments with great variations can be made without departingfrom the spirit and scope of the invention. It will be understood thatspecific embodiments described in the specification shall not beintended to limit the scope of the invention which shall solely belimited by the appended claims.

What is claimed is:
 1. A memory array, comprising: a plurality of memorycells; a plurality of paralleled bit lines formed on a semiconductorsubstrate, and a plurality of word lines perpendicular to the bit lines,wherein each bit line is connected to a source and a drain of adjacentmemory cells; a part of a word line between adjacent bit lines isconnected to a gate of a memory cell; wherein, the memory cells aresplit-gate memory cells, each comprising a first memory bit cellarranged between a word line and a source of the memory cell, and asecond memory bit cell arranged between the word line and a drain of thememory cell, the first and the second memory bit cells comprising afirst control gate and a second control gate, respectively; the memoryarray further comprises a plurality of first control lines and secondcontrol lines connected to the first control gates and the secondcontrol gates, respectively, each pair of first control line and secondcontrol line being arranged on both sides of a word line and beingparallel to the word line; wherein the first and second memory bit cellsshare one word line; reading voltages are applied to the word line, thefirst control gate, the second control gate, and the bit lines connectedto the source and the drain to read the memory bit cells; during areading operation to the first memory bit cell, reading voltages appliedto the word line, the first control gate, the second control gate, thebit line connected to the source and the bit line connected to the drainare from 0.5 V to 5 V, from 0 V to 3 V, from 0 V to 6 V, from 0 V to 0.5V and from 0.8 V to 3 V, respectively; and wherein during a readingoperation to the second memory bit cell, reading voltages applied to theword line, the first control gate, the second control gate, the bit lineconnected to the source and the bit line connected to the drain are from0.5 V to 5 V, from 0 V to 6 V, from 0 V to 3 V, from 0.8 V to 3 V andfrom 0 V to 0.5 V, respectively.
 2. The memory array according to claim1, wherein a part of a bit line forms the source and the drain ofadjacent memory cells connected to the bit line; a part of a word lineforms the gate of the memory cell connected to the word line.
 3. Thememory array according to claim 2, wherein the first memory bit cellfurther comprises a first floating gate, the first control gate beingspaced from and arranged above the first floating gate; the secondmemory bit cell further comprises a second floating gate, the secondcontrol gate being spaced from and arranged above the second floatinggate.
 4. The memory array according to claim 3, wherein the part of theword line forming the gate of the memory cell is isolated from thesemiconductor substrate, the first floating gate and the second floatinggate by a tunneling oxide layer; gate oxide layers are formed betweenthe first floating gate and the semiconductor substrate, as well asbetween the second floating gate and the semiconductor substrate.
 5. Thememory array according to claim 4, wherein the tunneling oxide layer isa silicon oxide layer or a silicon nitride layer or a combinationstructure thereof.
 6. The memory array according to claim 5, wherein thetunneling oxide layer has a thickness of 80-200 Å.
 7. The memory arrayaccording to claim 3, wherein interlayer dielectric films arerespectively formed between the first floating gate and the firstcontrol gate, between the second floating gate and the second controlgate, as well as between the word line and the first and second controlgates.
 8. The memory array according to claim 7, wherein the interlayerdielectric films are insulating dielectric films formed by one ofsilicon dioxide, silicon nitride, silicon oxynitride, andcarbon-containing silicon oxide or any combination structure thereof. 9.The memory array according to claim 3, wherein both the first floatinggate and the second floating gate are polysilicon floating gates orsilicon nitride floating gates or nano-crystal materials havingelectrical conductivity; both the first control gate and the secondcontrol gate are polysilicon control gates or metal control gates; theword lines are polysilicon selection gates or metal selection gates. 10.The memory array according to claim 3, wherein the word lines and thefirst and second control lines are all arranged below the bit lines. 11.The memory array according to claim 3, wherein the word lines and thefirst and second control lines are all arranged above the bit lines. 12.The memory array according to claim 1, wherein during the readingoperation to the first memory bit cell, the reading voltages applied tothe word line, the first control gate, the second control gate, the bitline connected to the source and the bit line connected to the drain are2.5 V, 2.5 V, 4 V, 0 V and 2 V, respectively.
 13. The memory arrayaccording to claim 1, wherein during the reading operation to the secondmemory bit cell, the reading voltages applied to the word line, thefirst control gate, the second control gate, the bit line connected tothe source and the bit line connected to the drain are 3 V, 3 V, 2.5 V,2 V and 0.5 V, respectively.